Assessm en t of heat exc hangers for coupling a high tem p erature n uclear reactor to h ydrog en and biofuels plan ts

Ad i t i V e r m a

Abs tr act

This pap er ou t l ines the design problem giv en to the studen ts of 22.033 and presen ts four heat exc hanger t yp es as candi dat e de si gns for t he pr o ces s heat sy st em. Rat i onal e for c ho osi ng a heat ex c hanger and mat er i al s concer ns ar e pr esen t ed a nd fut ur e w o r k i s a l so di scusse d.

1. Des ign Pr oblem

The studen ts of 22.033 aim to design a n uclear p o w er plan t whic h will b e coupled to h ydrogen and biofuels pro­ duci ng fa ci l i t i es b y mea ns o f hi g h t emp er a t ur e hea t ex ­ c hangers (HXs ) [1]. This pap er will presen t and discuss fo ur H X desi g ns t h a t ha v e b een sel ect ed b y t he Pr o cess He at te am as s tron g c an d id ate s . M ate rials c on c e rn s o f prosp ectiv e HX materials are outlined. Choice s of HX con­ fig ur a t i o ns a nd fut ur e w o r k a r e di scussed.

2. Pr o ces s Heat Sys tem

A lead co oled reactor with an outlet temp erature of 650 º C and a secondary lo op of sup ercritical CO 2 ha s b een c hosen b y the Core group. The heat pro vided b y the reac­ tor s h ou ld b e tran s p orte d to th e h yd roge n an d b iof u e ls f a­ cilities at minim um temp erature and pressure losse s. The pro cess h eat system will c o n sist of a single high temp e r­ atu re h eat exc h an ger or t w o h eat exc h an gers in th e sec­ on d ary lo op , h eat exc h an gers at th e h eat storage s y s t e m, bi o fuel s a nd h y dr o g en pl a n t s, a hea t st o r a g e sy st em a nd pi pi ng fo r t r a nsp o r t i ng t he w o r k i ng flui d t o t he h y dr o g en an d b iof u els f acilit y . Also u n d er con sid eration are h eat si nk opt i ons.

3. Heat Exc hanger Des igns

The applicabilit y of heat exc hanger designs to this sys­ te m w as e v alu ate d b as e d on th e f e as ib ilit y of th e h e at ex c hanger t ec hnol ogy as w el l op er at i ng t emp er at ur es and pr essur es. E ff ect i v eness, si ze, hea t t r a nsfe r a r ea p er uni t vo l u m e , wo r k i n g fl u i d o p t i o n s , h e a t l o s s e s a n d p r e s s u r e dr o ps fo r t h e v a r i o us desi g ns w er e a l so pr i ma r y co nsi der a ­ tion s . Of th e h e at e xc h an ge r d e s ign s s c re e n e d , f ou r d e s ign s we r e f o u n d t o b e m o s t p r o m i s i n g : S h e l l a n d S t r a i g ht t u b e hea t ex c ha ng er , Shel l a nd hel i ca l t ub e hea t ex c ha ng er , Plate t yp e heat exc hanger and Prin ted Circuit Heat Ex­ c hangers (PCHE). Not discussed here are heat pip es and

thermosyphons whic h w ere also review ed as p oten tial in­ te rme d iate h e at e xc h an ge r d e s ign s c ap ab le of p e rf ormin g heat transp ort func tions [2]. The principal features o f eac h desi g n a r e l i st ed i n T a bl e 1 .

3.1. Shel l and str aight tu b e he at Exchanger

These heat ex c hangers find extensiv e application in n u­ cl ear pl an t s and al so as pr o cess heat sy st ems and can b e desi g ned t o b e v er y r o bust a nd sui t a bl e fo r sp eci a l o p er ­ ating conditions suc h as a radioactiv e en v ironm en t. They can b e fabricated using Hastello y , Incolo y , graphite and p olymers [4]. The design can b e adapted to inc lude fins if on e o f th e w orkin g fl u id s is gas e ou s an d th e h e at e x­ c hanger allo ws liquid/liquid, gase ous/liquid as w ell as t w o phase systems. These heat exc hangers are v ery large due to lo w heat transfer area p er unit v olume (~100 m 2 /m 3 ) but a l l o w hi g h o p er a t i ng t emp er a t ur es ( up t o 9 0 0 º C) and pr essur es ( u p t o 3 0 MP a ) .

3.2. Helic al t yp e He at Exchanger

The shell and helical tub e heat exc hanger is a v ariation on th e sh ell an d straigh t tu b e h e at exc h an ger d esign an d consi st s of t ub es spi r al l y w ound and fit t ed i n a she l l . Spi r al tu b e ge ome try p ro vid e s a h igh e r h e at tran s f e r ar e a p e r u n it vo l u m e ( 2 0 0 m 2 /m 3 compar ed t o 100 m 2 /m 3 fo r st r a i g h t shell and tub e t yp e HXs). This design has b een p r o v en b y its u s e in th e High T e mp e ratu re E n gin e e rin g T e s t Re ac tor (HTTR) [5 ] . Helical t yp e heat exc hangers are w ell suited to gas e ou s /liqu id s ys te ms . A d is ad v an tage of th is d e s ign is th e d i ffi c u lt y of c le a n in g th e h e lic al c oils [6, 3].

3.3. Plate T yp e He at Exchanger

In a plate t yp e heat exc hanger, the heat transfer o ccurs th rou gh p lan ar s u rf ac e s . P late t y p e HXs allo w c ou n te r, cr oss and par al l el flo w configur at i ons [ 7] and can b e fabr i ­ cated from Hastello y and Ni Allo ys. These heat exc hang­ er s al l o w b ot h m u l t i pass and m ul t i st r eam capabi l i t i es and greatest ease of clean in g an d main ten an c e as comp ared to the other designs review ed in this pap er. There are sev eral

Pr e print s ub m it t e d t o Els e v ie r Octo b er 1 7 , 2 0 1 1

T ab l e 1: Principal F eatures of Heat Exc hangers (adapted from [3])

HX T yp e	Compactness	T. Range	Max P .	Mul t i str ea m	Mul t i pass	Cleaning Metho d
	(m 2 /m 3 )	( º C)	(M P a)
Shel l a nd T ub e	~100	~+900	~30	No	Ye s	Mec hanical, Chemical
Pl a t e	~200	-35 to ~+900	~60	Ye s	Ye s	Mec hanical, Chemical
He lical	~200	~600	2.5	No	No	Mec ha ni ca l
Prin ted Circuit	2000 to 5000	-200 to ~+900	~60	Ye s	Ye s	Chemical

va r i a t i o n s o n p l a t e t y p e d e s i g n s a n d t h e B a v e x p l a t e H X pr o v i des t he hi g hest o p er a t i ng t emp er a t ur es ( up t o 9 0 0 º C) [3, 6].

3.4. Printe d Cir cu it He at Exchanger (PCHE)

PCHEs can op erate under high temp erature (~1000 K) and high pressure conditions. They are t ypically used in p e tro c h e mic al, re fi n in g, an d u p s tre am h yd rop ro c e s s ­ ing industries. PCHEs can incorp orate m ultiple pro cess st r eams i n t o a si nge uni t and ha v e l o w mass/dut y r at i os of ~0.2t/MW [8]. They are s uitable for corrosiv e en viron­ men ts and ha v e e ff ectiv enesses of up to 98%. In a PCHE the fluid flo w c hannels, whic h are of the order of sev e r al millimeter s, ar e c hemically etc hed and the flo w can b e par ­ allel, cross or cou n ter fl o w or a com b in ation of all th ree. Ab s e n c e of gas k e t an d b raz e mate rial lo w e rs th e p rob ab il­ it y of le ak a ge [9]. Ho w e v e r, th e re is p ote n tial f or th e rmal stresses in the axial d ir e ction when there are sharp tem­ pe r a t u r e v a r i a t i o n s a n d t h i s d e s i g n a l s o s u ff e r s f r o m l o w capaci t y fact or s due t o t he need for o ffl i ne i nsp ect i on and re p airs [10]. S m all fl o w c h an n e ls c ou ld re s u lt in f ou lin g problems whic h w ould require o ffl ine repairs using c hem­ ic al me th o d s [3]. Ho w e v e r, re d u n d an t mo d u le s ma y b e in s talle d to imp ro v e c ap ac it y f ac tors of th e p ro c e s s h e at system during main tenance and repairs. PCHEs ha v e not be e n u s e d f o r p r e v i o u s l y f o r n u c l e a r a p p l i c a t i o n s b u t a r e under r ev i ew a s p o t en t i a l H X s fo r t he N ex t G ene r a t i o n Nu c le ar P lan t [11].

4. Mater ials concer ns

It is imp erativ e that the materials c hosen for fabricat­ in g h e at e xc h an ge rs f or th e p ro c e s s h e at s ys te m are ab le to withs t and op erating conditions of high tem p eratures (u p to 900 º C) and press ures. Susceptibilit y of candidate mater ials to str ess cor r o s ion cr ac king under constan t load as w ell as slo w-strain-rate conditions, fracture toughnes s and crac k gro wth b eha vior has b een studied and litera­ tu re in d ic ate s th at Allo y 230 an d Allo y 617 are s u itab le for fabricating high temp erature heat exc hangers [12]. The op eratin g con d ition s f or th e h eat exc h an ger at th e h yd ro­ gen plan t will b e more sev ere due to temp eratures higher th an th e c ore ou tle t te mp e ratu re . S tu d ie s in d ic ate th at Allo y C-22 and Allo y C-276 b ec ause of their high tensile st r engt h and duct i l it y un t i l fr act ur e ar e sui t abl e heat ex ­ ch a n g e r m a t e r i a l s f o r h e a t e x c h a n g e r s o p e r a t i n g i n o r n e a r

acidic en viro n men ts [13]. F uture w ork wil l require c ho os­ in g h e at e xc h an ge r d e s ign s a n d mate rials f or e ac h d e s ign .

5. Heat Exc hanger Configur ations

The heat exc hangers ma y b e connected in series or in parallel with the p o w er con v ersion system. The series con­ figurations will a l lo w extraction of the heat from the su­ p ercritical CO 2 at th e h igh est p ossib le temp eratu re b u t at a p o w e r c o n v e r s i o n e ffi c i e n c y p e n a l t y . A p a r a l l e l c o n fi g u ­ ration will allo w supplying the w orking fluid at equal tem­ pe r a t u r e s t o bo t h t h e po w e r c o n v e r s i o n a n d p r o c e s s h e a t systems but eac h system will receiv e smaller flo w rates of the w orking fluid. F urthermore, whe ther c o n nected in se­ ries or in parallel with the p o w er con v ersion system , the HX connected to the CO 2 lo op c an c on s is t of e ith e r a s in ­ gle h eat exc h an ger or a t w o stage h eat exc h an ger system consi st i ng of a hi gh t emp er at ur e and a l o w t emp e r at ur e hea t ex c ha ng er . A t w o st a g e sy st em w o uld r ed uce co st s by e l i m i n a t i n g t h e n e e d f o r a s i n g l e l a r g e h e a t e x c h a n g e r ha v i ng a l o ng desi g n l i fe but w o ul d a dv er sel y a ff ect t he con t r ol l abi l i t y of t he sy st em and i ncr ease heat l osses [ 10] .

6. F uture W o rk

The c hoice of heat exc hangers, heat exc hanger materi­ als an d con fi gu ration s are go v ern ed b y th e w orkin g fl u id used i n t he pr i ma r y cy cl e a nd t he t emp er a t ur es, pr essur es, temp erature and pressure drops and flo w rates at whic h pro cess heat will b e required at the h ydrogen and biofu­ el s pl an t s. Based on t hese consi der at i ons heat ex c hanger designs and configurations will b e c hosen from among the four designs discussed in this pap er. The heat exc hange r design and configuration th us c hosen will then b e mo deled using MA TLAB, EES o r RELAP5 or a com bination of the three and the pro cess heat system will b e optimized for this design problem. F uture w ork will also study pressure dr o ps a sso ci a t ed w i t h ca ndi da t e desi g ns.

Refer ences

[1] Mic hael Short. 22 . 0 33 syllabus, 2011.

[2] Viv ek Utgik ar F red Gunnerson Piyush Sabharw all, Mik e P atter­ son. Phase c hange h eat transfer device for pro cess heat applica­ tions. Nuc le ar Eng ine e ring and D e s ig n , 2 4 0 : 2 4 0 9 – 2 4 1 4 , 2 0 1 0 .

[3] Dusan P .Sekulic Ramesh K.Shah. Fu n d a m e n t a l s o f H e a t E x ­ ch a n ger Desi gn . John Wiley and Sons, 2003.

[4] M.T ak ey ama R T anak a T.Matsuo, M.Uk ei. Strengthening of nic k el-based sup erallo ys for n uclear heat exc hanger ap pli cation s. Jo ur n a l o f N ucl e a r Ma ter ia l s , 2 2 : 1 9 0 1 – 1 9 0 7 , 1 9 8 7 .

[5] H.G. Gro ehn. Thermal h ydraulics of helical-t yp e helium/helium in termediate heat exc hangers (ihxs) for n uclear pro cess heat ap­ plications of high temp erature gas-co oled reactors-fundamen tal researc h and large scale tests. Nuc le ar Eng ine e ring and D e s ig n , 126:285–290, 1991.

[6] Mic hael McKellar Nolan Anderson Piyush Sabharw all, Eung So o Kim. Pro cess heat exc hanger options for fluoride salt high temp er a tur e reactor. T ec hnical rep ort, I d aho National Labs, 2011.

[7] Y.Chen S . R. Sherman. Heat exc hanger testing requiremen ts and facilit y needs for the nhi/ngnp pro ject. T ec hnical Rep ort WSR C -S T I -2008-00152, 2008.

[8] Heatric tm, 2011. URL www.heatric.com .

[9] K.Natesan S.Ma jumdar, A.Moisseytsev. Assessmen t of next generation n uclear plan t i n termediate heat exc hanger design. T ec hnical rep ort, Argonne National Lab oratory , 2008.

[10] Eung S.Kim Cha ng H. Oh. Design option of heat exc hanger for next generation n u clear plan t. T ec hnical r ep ort, I daho National Lab orator y , 2008.

[11] Nolan A. Anderson Prashaan th Ra vindran, Piyush Sabharw all. Mo d el ing a prin ted circuit heat exc hanger with relap5-3d for the next generation n uclear plan t. T ec hnical r ep ort, I daho National Lab oratory , 2010.

[12] An thon y E. Hec hano v a. High temp erature heat exc hanger pro ject. T ec hnical rep ort, U NL V Researc h F oundation, 2008.

[13] Narendra K othapalli Ragh unandan Karamc heti Ajit Ro y , Lalit Sa v alia. Mec hanical prop erties and crac king b eha vior of high-temp erature heat-exc hanger materials. I n Pr o c e e ding s of th e A S ME P r essur e V essel s a n d P i p i n g Co n f er e n c e 2 0 0 5 , V o l 6 , 2 0 0 5 .

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22.033 / 22.33 Nuclear Systems Design Project

Fall 2011

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